Low density material containing a vegetable filler

ABSTRACT

A process for reducing the density, increasing the bulk, the hand and the porosity of a sheet material containing fibers by use of a vegetable filler, wherein a pulverulant vegetable filler of density less than 500 kg/m 3  is introduced into the fibrous mass during the manufacture of the material. At least 95% by weight of the particles of the vegetable filler are less than 150 micrometers in size and at least 80% by weight of the particles of vegetable filler are greater than 10 micrometers in size. The process is particularly useful for obtaining paper and cardboard of low density with improved hand (or bulk) and porosity. It is also attractive since it reduces the cost prices and enhances the thermal and acoustic insulation properties.

This is a continuation of application Ser. No. 07/397,428, filed Aug. 8,1989 which was abandoned upon the filing hereof.

BACKGROUND OF THE INVENTION

The present invention relates to the use of a vegetable filler of lowdensity and controlled particle size. It relates more particularly tothe preparation of a composite sheet material, containing fibers, whichis more porous and has a reduced density with an improved bulk by virtueof such a vegetable filler. It is of particular value in the field ofthe manufacture of fibrous sheets such as paper, board and othernonwovens.

It is conventional in papermaking to use mineral, organic or syntheticfillers or pigments. The most commonly used mineral fillers and pigmentsare talc, kaolin, natural and precipitated calcium carbonate or calciumcarbonate originating from the operations for regenerating the blackliquor extracted from the digestion of kraft pulps, magnesium carbonate,alumina hydrates, calcium sulfate, colloidal silica, barium sulfate,titanium dioxide, magnesium hydroxide and mixtures thereof.

The conventional fillers used in papermaking have variable equivalentspherical diameters, measured by means of the SEDIGRAPH device, but as ageneral rule all these fillers have particles with dimensions smallerthan 100 micrometers, in particular smaller than 50 micrometers andespecially smaller than 30 micrometers.

Thus 50% of the particles of the kaolin to be incorporated into the masshave a size of between 6 and 8 micrometers (d₅₀ =6-8 micrometers) and95% of the particles have a size of less than 50 micrometers (d₉₅ <50micrometers). The talc to be incorporated into the mass has a d₅₀ ofbetween 8 and 10 micrometers and a d₉₅ of less than 50 micrometers andthe calcium carbonate has a d₅₀ of between 7 and 9 micrometers and a d₉₅of less than 25 micrometers.

The surface-coating pigments have a d₅₀ of between 1 and 3 micrometersand a d₉₅ of less than 10 micrometers. The organic pigments are muchfiner and have a d₅₀ of between 0.1 and 1 micrometer.

It is known, especially from EP-B-0 006 390, EP-B-0 050 316 and FR-A-2578 870, that mineral fillers favor a lowering of the material cost and,depending on their nature, favor the opacity, in particular in thesector of printing-writing substrates and certain special types ofpaper. If the proportion of mineral fillers in the material is highcompared with that of the cellulosic fibers, they can favor thedimensional stability, which is particularly desirable in bases forfloor or wall covering; however, on the one hand the use of thesemineral fillers has an adverse effect on the thickness of the material,and on the other hand the increase in the residual ash content alsoresults in a substantial increase in the density of the material, whichdoes not favor the cost per m².

The paper industry uses certain special fillers or pigments to increasethe thickness of the sheet, for example diatomite or natural, calcinedor activated diatomaceous earths, carbon or glass microspheres, calciumsilicates and colloidal silicas, but these fillers or pigments aregenerally very expensive.

The incorporation of so-called mechanical cellulosic pulps, such asthermomechanical or chemicomechanical pulps, and, to a lesser extent,mercerized pulps and synthetic fibers, especially polyester,polyethylene and polypropylene fibers, also plays a part in improvingthe bulking (or body of paper or puffing out), but the use of thesefibers demands substantial industrial means and only concerns veryspecific applications.

It is known that the possibility of using wood powder or flour as afiller, introduced into the mass or deposited on the surface by coating,in the manufacture of paper and board has already been indicated in thepast.

It is known in particular that abstract no. 8739 of the journal ABSTRACTBULLETIN OF THE INSTITUTE OF PAPER CHEMISTRY, 48, (no. 8), page 938,(February 1978), U.S. Pat. No. 3,184,373 and German patent DE-C-415 675provide for the incorporation of wood powder into the fibrous mass.

Abstract no. 8739 mentioned above recommends the use of a mixture of70-95% by weight of cellulosic pulp (kraft fibers) and 30-5% by weightof wood flour for the manufacture of electrically insulating panels,these panels being said to be more absorbent towards oils and moreresistant to surface discharges. The said document neither describes norsuggests the use of a vegetable filler having the particle size anddensity specific to the present invention.

U.S. Pat. No. 3,184,373 relates to the improvement in the retention offillers in paper and board by means of a retention agent such aspolyethyleneimine, melamine-formaldehyde resins and urea-formaldehyderesins, the said "fillers" being defined (see column 2, lines 3-34) asbeing solid or liquid substances and comprising, in particular, mineralpaper fillers themselves, metal powders, thermosetting resin powdersthermoplastic resins, binders, flocculants and wood powder (see column2, line 27). The particle size of the said "fillers" is said to bebetween 60 mesh and 2000 mesh (see column 1, lines 70-71). However, U.S.Pat. No. 3,184,373 does not give any Examples illustrating the use ofthe said wood powder introduced into the mass; furthermore, it neitherdescribes nor suggests the particle size (particle dimensions of between10 and 150 micrometers) and the density (less than 500 kg/m³) specificto the vegetable filler according to the invention.

German patent DE-C-415 675 proposes a sizing process in which (i) acolloidal dispersion of a submicron substance (i.e. a substance with aparticle size of less than 1 micrometer) containing cellulose andoriginating from the grinding of wood or straw, and then (ii) aflocculant, are incorporated into an aqueous suspension of fibers. Thesaid submicron substance, which therefore has a particle size well belowthat of the vegetable filler according to the invention, fulfils atotally different role from that of the said vegetable filler; in fact,the said submicron substance is presented in German patent documentC-415 675 as reducing the porosity of the resulting paper by blockingand/or filling the pores in the fibrous web, whereas an increase in theporosity is sought according to the invention.

Techniques of covering (on a non-fibrous substrate) or surface sizing(on a fibrous sheet substrate such as paper and board) are known fromother sources, especially from Belgian patent BE-A-425 432, publishedPCT International application WO 86/05195 and British patent GB-A-1 464381, wherein a substrate is coated with a composition containing woodpowder. It so happens that these techniques neither describe nor suggestthe incorporation, into the fibrous mass, of the vegetable filler ofspecific particle size and density according to the invention.

Products which are capable of being incorporated into paper and board,contain cellulose and are obtained by the physicochemical treatment ofwood chips or cellulosic fibers are also known, especially from abstractno. 1523 of the journal ABSTRACT BULLETIN OF THE INSTITUTE OF PAPERCHEMISTRY, 58 (no. 2), page 184 (August 1987), abstract no. 7191, ibidem55 (no. 6), page 754, (December 1984), and published French patentapplication FR-A-2 612 828 (which was made public on Sep. 30, 1988,after the priority date of the present invention). The composition ofthe said products containing cellulose is different from that of thevegetable or fibrous source from which they are derived. In fact, thephysical and chemical treatments to which the said source has beensubjected do not preserve the integrity of the components of the saidsource.

More precisely, abstract no. 1523 mentioned above describes thepreparation of cellulose in the form of micronized particles (having asize of between 5 and 75 micrometers and a degree of crystallinitygreater than 65%) by the hydrolytic treatment of cellulosic pulps. Thecellulose obtained in this way differs from the composition of thevegetable filler according to the invention in respect of the nature ofthe components of the latter.

Abstract no. 7191 mentioned above describes the use of microfibrillatedcellulose for the production of coatings for covering. Here again themicrofibrils of cellulose differ in their structure and composition fromthe vegetable filler according to the invention.

French patent document FR-A-2 612 828 is deceptive in the sense that itsclaim 1, as published, refers to the use of wood particles in thepreparation of fibrous sheets, whereas what is actually involved is theuse of an extract, in pulverulent form, obtained by treating woodpowder, the said treatment comprising the following steps in particular(see descriptive part of the said document from page 1, line 28, to page2, line 12): (i) impregnation of the wood powder with an appropriateliquid chemical agent (sic), (ii) flash autolysis (or flashautohydrolysis) of the impregnated wood powder under a pressure greaterthan or equal to 30 bar, at a temperature greater than or equal to 230°C., for at least 90 seconds, followed by a rapid (sudden) release ofpressure, (iii) washing of the resulting product with water or awater/dioxane mixture in order to remove the hemicelluloses and most ofthe lignin, fatty acids and resin acids, and then (iv) drying of theextracted pulverulent product containing water-insoluble materials anddevoid of water-soluble materials.

The present invention differs from the teaching of the said abstractsno. 1523 and no. 7191 and the said French patent document FR-A-2 612 828by the fact that the vegetable filler, which it is recommended to use inthe mass, has preserved substantially all the components of thevegetable source; in the vegetable filler according to the invention,only the water content and the content of volatile substances (such asthe low-boiling essential oils) have been affected by comparison withthe starting vegetable source. Thus, if the vegetable source is wood,practically all the components of the wood, as described in the work byFENGEL et al., WOOD CHEMISTRY ULTRASTRUCTURE REACTIONS, pages 26-33,published by D. GRUYTER (1984), which is incorporated here by way ofreference, will be found in the vegetable filler.

Referring to the teaching of the nearest prior art, which consists ofabstract no. 8739 of the journal ABSTRACT BULLETIN OF THE INSTITUTE OFPAPER CHEMISTRY, 48, (no. 8), page 938, (February 1978), U.S. Pat. No.3,184,373 and German patent DE- C-415 675 mentioned above, it should bepointed out that the use of wood flour or powder has never worked on theindustrial scale according to precise specifications (i) for the densityand particle size of the vegetable filler, and (ii) for the purpose ofobtaining, by a papermaking technique, sheets of fibrous materials whichare more economical and have a lower density, with a high porosity and ahigh bulk.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel technicalsolution for overcoming the above-mentioned difficulties. This solutionutilizes an abundant and renewable vegetable raw material, namely woodand principally waste wood, as well as other vegetable waste such as, inparticular, waste from cereal production, especially maize cobs. It isthis vegetable raw material which will be used to manufacture thelow-density vegetable fillers having the desired particle size so thatthey can be incorporated into the mass, either direct like any otherconventional filler used in papermaking, or, preferably, in the form ofa previously flocculated mixture of filler and binder.

Thus, according to one of its aspects, the present invention relates tothe manufacture of a sheet material by a papermaking technique, thematerial containing a vegetable filler of low density and controlledparticle size, making it possible to reduce the density and increase thethickness, bulk and porosity of this material.

Furthermore, according to the invention, the reduction in density andthe increase in thickness of the material impart specific and beneficialproperties, such as opacity and acoustic thermal and electricalinsulation, especially in the case of fibrous sheets.

In addition, according to the invention, the use of the above-mentionedvegetable filler favors the rate of drainage during the manufacture ofthe sheet material and hence favors productivity. The present processalso has the advantage of lowering costs.

According to the invention, it is recommended to use a vegetable fillerof specific particle size and density for the manufacture of fibroussheet materials by a papermaking technique, utilizing a technicalsolution which differs from the teaching of the prior art by the choiceof the said vegetable filler of specific density and particle size.

In this technical solution, the vegetable filler of specific density andparticle size is introduced into the mass.

As a variant, it is recommended to replace part of the fibers(expensive) of the fibrous sheet material with the said vegetable fillerof specific density and particle size (less expensive).

According to the invention, a novel technical solution is proposed whichmakes it possible to reduce the density, increase the porosity, increasethe bulk and lower the manufacturing costs of paper and board.

This novel technical solution also makes it possible (i) to increase thethickness of the fibrous sheet material on account of the reduction indensity, (ii) to improve the bulking of the said material, and (iii) toimprove drainage on the paper machine during the formation of the saidmaterial.

One of the fundamental characteristics of the process according to theinvention is the use of a pulverulent vegetable filler having a densityof less than 500 kg/m³ and preferably of less than 300 kg/m³, on the onehand, and a d₉₅ of less than 150 micrometers and a d₈₀ of more than 10micrometers [i.e. at least 95% of the particles of vegetable filler(percentage expressed by weight) pass through a square-mesh sieve (madeespecially of stainless steel) with a mesh size of 150×150 micrometers,and at least 80% of the particles do not pass through a square-meshsieve (made especially of stainless steel) with a mesh size of 10×10micrometers, on the other hand.

According to a first aspect of the invention, a process is thereforeprovided for the preparation of a fibrous sheet material by apapermaking technique, in which process, which comprises introducing apulverulent vegetable filler into an aqueous dispersion containingfibers, the vegetable filler is micronized, has a density of less than500 kg/m³ and has a particle size such that (i) at least 95% by weightof the particles of the said vegetable filler have dimensions smallerthan 150 micrometers, and (ii) at least 80% by weight of the particlesof the vegetable filler have dimensions larger than 10 micrometers.

According to a second aspect of the invention, a process is provided forreducing the density of a fibrous sheet material by means of a vegetablefiller, wherein a pulverulent vegetable filler which has a density ofless than 500 kg/m³ and a particle size such that (i) at least 95% byweight of the particles of the said vegetable filler have dimensionssmaller than 150 micrometers, and (ii) at least 80% by weight of theparticles of the said vegetable filler have dimensions larger than 10micrometers, is introduced into the aqueous suspension containing fibersduring the manufacture of the said material.

In other words, through the use of the said vegetable filler, theinvention provides a process for increasing the thickness, bulk andporosity, on the one hand, and reducing the density of the material, onthe other. Using the vegetable filler has a very favorable effect ondrainage and has the advantage of lowering the production costs.

DETAILED DESCRIPTION OF THE INVENTION

Any species of wood can be used to obtain the vegetable filler accordingto the invention, such as wood from coniferous trees like fir, pine andspruce, and wood from deciduous trees such as birch, beech, hornbeam andchestnut. These woods can originate either from clearance felling orfrom tree stubbing, after conversion to chips or strips/platelets by themethods well known in the paper industry for the manufacture of chemicaland chemicomechanical pulps. For essentially economic reasons, thesevegetable fillers will originate from waste produced in the wood cuttingand planing industry, such as fresh and dry sawdust, planing chips, barkand machining debris produced in parquetry, joinery and cabinet making.

The vegetable filler can also be obtained from waste vegetable materialproduced in forestry, such as tree stumps, unutilized branches of smalldiameter, remnants and the top ends of tree trunks, and also from wasteproduced in cereal harvesting, such as maize cobs.

As the various vegetable sources mentioned above have differentphysical, chemical and morphological properties, the properties whichthey impart to the final fibrous sheet material can vary, as regards thedensity, bulk and porosity, according to the species used. Nevertheless,a significant reduction in the density and an increase in the bulk andporosity are obtained in all cases.

It is important for the micronized vegetable filler to be in the form ofparticles having mean dimensions smaller than 150 micrometers (d₉₅ <150micrometers) and greater than 10 micrometers (d₈₀ >10 micrometers). Infact, if the particles of micronized vegetable filler have meandimensions equal to or larger than 150 micrometers, the resultingfibrous sheet product exhibits uniformity defects, especially formationdefects; if the particles of micronized vegetable filler have meandimensions smaller than or equal to 10 micrometers, the resultingfibrous sheet product is distinctly less porous, as taught by Germanpatent DE-C-415 675 mentioned above. As indicated earlier, the particlesize of the micronized vegetable filler will be such that d₉₅ <150micrometers (preferably d₉₅ <100 micrometers) and d₈₀ >10 micrometers.

Furthermore, it is also important, as regards the properties requiredfor the final sheet product, for the density of the micronized vegetablefiller to be less than 500 kg/m³ and preferably less than 300 kg/m³.

To obtain the vegetable filler according to the invention, it is alsoimportant for the vegetable source, which is subjected to agrinding-micronization operation, to have a particle size less than orequal to 5 mm and a residual moisture content of less than 20% prior tothe grinding-micronization operation.

In the process of the invention, the vegetable waste is subjected to agrinding-micronization operation in order to produce the vegetablefillers with the particle dimensions required for the subject of theinvention. This result is achieved by a specific grinding-micronizationtechnique (vegetable source with a particle size less than or equal to 5mm and a residual moisture content of less than 20%), especially bymeans of a disk-type grinder-selector with impact beaters, which makesit possible, through intense high-speed collisions and with changes inpressure, to cause the gradual disintegration of the vegetable sourceuntil the desired fineness and density are obtained. Advantageously, theresidual moisture content of the vegetable source to be subjected to thegrinding-micronization operation will be less than or equal to 15%.

Thus, if the vegetable source (or raw material) takes the form ofstrips/platelets, planing chips, machining debris, branches etc., it isfirst necessary to shred it and, if appropriate, dry it, before thegrinding-micronization operation, in order to obtain a fineness lessthan or equal to 5 mm and a residual moisture content of less than 20%.

In paper applications, the vegetable fillers according to the inventionwill therefore have a d₉₅ of less than 150 micrometers (i.e. at least95% of the particles of vegetable filler pass through a square-meshsieve of 150 micrometers by 150 micrometers), preferably a d₉₅ of lessthan 100 micrometers. These vegetable fillers will be associated with anatural or customary organic binder, fibers and various additivesconventionally used for the preparation of fibrous sheets.

The weight ratio pulverulent vegetable filler/fibers according to theinvention will generally be within the range from 1/100 to 6/1. For themanufacture of wrapping paper, it will be advantageous to use a weightratio vegetable filler/fibers within the range from 1/100 to 2/10 (andpreferably from 1/100 to 1/10), for the manufacture of printing-writingsubstrates a weight ratio within the range from 2/10 to 5/10 (andpreferably from 2.5/10 to 3.5/10), for the manufacture of cardboard aweight ratio within the range from 1/10 to 5/10, for the manufacture ofpaper for impregnation a weight ratio within the range from 1.5/10 to5/10 (and preferably from 2/10 to 3/10) and for the manufacture ofspecial types of paper a weight ratio within the range from 6/100 to 6/1(and preferably from 3/10 to 8/10).

The fibers which can be used for these various applications are, inparticular, natural or synthetic organic fibers such as cellulosicfibers, polyamide fibers, polyester fibers, polyalkylene fibers andpolyacrylate fibers, mineral fibers such as glass fibers, ceramicfibers, acicular gypsum fibers, carbon fibers and rock wool, andregenerated cellulose fibers. These fibers can be used on their own orin a mixture. The fibers most commonly used will be cellulosic fibersoriginating from kraft or bisulfite chemical pulps, mechanical pulps,thermomechanical pulps or chemicothermomechanical pulps. These pulps,produced from species of conifercus or deciduous trees, can beunbleached, semi-bleached or bleached.

It is also possible to use so-called recovered cellulosic pulpsoriginating from waste paper (such as printing-writing substrates,newspapers, cardboard boxes, wrapping paper, magazines and the like), bythemselves or in association with noble cellulosic fibers.

In the process of the invention, the vegetable fillers of controlledparticle size can be associated with other organic or synthetic mineralfillers or mixtures thereof; these customary or special fillers orpigments used in papermaking are those which have already been mentionedabove.

In practice, according to the invention, the vegetable filler will onthe one hand replace part of the essential ingredient of the material,namely the fibers in the paper sector, and on the other hand be able toreplace all or only a fraction of the customary filler, especiallymineral filler, in the material.

In paper manufacture, it can be advantageous to incorporate, into thefibrous mass containing the vegetable fillers, one or more agentsconventionally used in papermaking for increasing the dry strengthproperties of the sheet, for example native starches or starchesmodified by a chemical, enzymatic or thermal method, dextrins, polyvinylalcohols, casein, animal size, vegetable proteins, cellulose esters suchas carboxymethylcellulose, alginates, dispersions of syntheticpolyamines, carboxylated or non-carboxylated styrenebutadiene latices,acrylic latices, styrene-acrylic latices, vinyl acetate latices,neoprene latices, acrylonitrile latices, vinyl chloride latices andmixtures thereof.

The amount of these natural or synthetic organic polymers which act as amass or surface binder can vary within very wide limits, according tothe applications, but as a general rule it is between 0.1 and 10 partsby dry weight of binder per 100 parts by weight of fibers for theconventional applications and especially for wrapping paper andcardboard and printing-writing paper, but it can be much higher, i.e.between 10 and 50 parts by weight and preferably between 10 and 30 partsby dry weight per 100 parts by weight of the fibrous sheet for specialapplications such as bases for making composites, for coating and forcoverings.

It may also be necessary to improve the wet strength properties of thefibrous sheets according to the invention, especially with additivescustomarily used in papermaking, such as urea-formaldehyde andmelamineformaldehyde resins, glyoxal, polyalkyleneamines, especiallythose which are cationic and crosslinked, and condensation products ofmelamine-formaldehyde and aminocaproic acid.

In addition to fibers and vegetable fillers, by themselves or combinedwith other fillers or pigments, in the presence or absence of natural orsynthetic organic polymers for improving the dry and wet properties, itis also possible to use:

sizes used in the paper industry for reducing the sensitivity of thepaper to water, such as modified rosins, paraffin emulsions and dimericalkylketens;

pH regulators such as aluminum sulfate and sulfuric acid; and

anionic and/or cationic retention agents for reducing the materiallosses during the formation of the sheet.

The following may be mentioned in particular: polyethyleneimine,polyamidoamine and polyalkylamine resins, especially those which arecrosslinked, polyacrylamide resins, especially modified polyacrylamideresins, and quaternary ammonium compounds.

Other customary additives used in papermaking are also possible:

antifoams;

fluorescent whiteners;

colorants or toners; and

fungicides and/or bactericides.

According to another aspect of the invention, these vegetable fillerscan first be subjected to a chemical treatment for giving themappearance properties and physical or chemical characteristics whichthey do not have in the natural state, before they are introduced intothe mass. Examples which may be mentioned are treatments which have aneffect on modifying the color of the wood particles, fungicidal,bactericidal and fireproofing treatments or treatments which favor areduction in the sensitivity of the vegetable material to water.

A sheet containing the vegetable fillers according to the invention canbe produced on a conventional paper or board machine with one or moreflat, inclined or vertical beds which may or may not be equipped withsingle-wire or twin-wire formers of circular shape. This sheet can be ofthe single-ply type or of the multi-ply type with plies of identical ordifferent compositions, as is the case for board in particular.

The fibrous sheet according to the invention, containing vegetablefillers, can also be subjected to different surface treatmentsconventionally used in papermaking, on or off the paper machine, withthe surface sizing, impregnating, coating and surface coating meansknown to paper manufacturers and processors.

The vegetable filler according to the invention can be used in the massand on the surface during the manufacture of the fibrous sheet. It isintroduced into the mass either direct, like any other conventionalpaper filler, or, preferably, in the form of a mixture of vegetablefiller and organic binder which has first been homogenized and thenflocculated (especially by means of a multistage flocculator) beforebeing incorporated into the aqueous suspension of fibers upstream of theheadbox. If necessary, it is applied to the surface of the fibrous sheetby customary methods of treating the surfaces of paper and board,especially by coating, surface coating and/or impregnation, inaccordance with the prior art mentioned above (especially Belgian patentBE-A-425 432, International patent application WO 86/05 195 and Britishpatent GB-A-1 464 381).

The vegetable filler according to the invention can be used direct inthe field of the preparation of coatings and paints. The essential aimis to reduce the density of the material. The secondary aims, which arealso of value, are to increase the thickness of the material and toimprove the bulking of the material and the beneficial properties interms of improving the opacity and the acoustic, thermal and electricalinsulation.

The best mode for carrying out the invention for paper and cardboardapplications has been given below

Stage 1

The cellulosic fibers in aqueous suspension are refined in conventionalmanner to a Schoepper-Riegler freeness of between 15 and 70 degrees,according to the applications, at a variable concentration of between 20and 350 g/l, in particular of between 20 and 60 g/l, with the aid ofstandard conical or twin-disk refiners, or especially of between 250 and350 g/l with special refiners for so-called high-consistency refiningused for the manufacture of wrapping substrates. If necessary, othertypes of synthetic or mineral fibers, by themselves or in association,can be introduced at this stage. In particular, glass fibers are usefulfor improving the dimensional stability of the sheet.

At this stage, the fibrous composition can be invariable if it is usedto manufacture a single-ply sheet, or variable if it is used tomanufacture a multi-ply sheet, as is the case for board in particular.

Stage 2

The vegetable fillers are produced from vegetable waste and mainly fromwaste produced in the timber industry and forestry. This waste willgenerally be subjected to an initial shredding-grinding operation, whenit is the form of large pieces, to give a vegetable raw material havinga particle size such that d₉₅ <5 mm before the finalgrinding-micronization operation. This is the case in general formachining debris, sawing trimmings, planing chips, small branches, treestumps, bark and maize cobs. The initial shredding-grinding treatment isnot necessary when the vegetable waste is sawdust; when the vegetablematerial is wet (the average moisture content is generally of the orderof 30%), it has to be dried to a residual moisture content less than orequal to 15% before the grinding-micronization operation in order toproduce vegetable fillers with the particle size and density requiredfor the applications according to the invention.

These vegetable fillers will have a d₉₅ of less than 150 micrometers andespecially a d₉₅ <100 micrometers, i.e. at least 95% of the woodparticles will pass through a square-mesh sieve of 150 micrometers by150 micrometers or, respectively, a square-mesh sieve of 100×100micrometers. These vegetable fillers can originate either from agrinding-micronization unit on the paper or board production site, orfrom an external unit.

The vegetable fillers are easily transported to the storage unit bymechanical means involving conveyor belts or screw conveyors, or bypneumatic means, before they are used on their production site by anintegrated plant or before they are supplied to external customers inbags, loose or semi-loose.

Stage 3

The vegetable fillers of the desired particle size can be introduceddirect into the mass, like a conventional paper filler. The amount ofvegetable fillers can vary from 1 to 50 parts by weight and especiallyfrom 1 to 30 parts by weight per 100 parts by weight of fibers in thecase of conventional wrapping or printing-writing paper or board, but itcan also vary from 60 to 600 parts by weight of vegetable fillers per100 parts by weight of fibers in the case of special applications suchas substrate for coating and impregnation for construction materials andwall and floor coverings.

These vegetable fillers can also be introduced into the mass with priormixing, homogenization and, if appropriate, flocculation of the fillerwith an organic binder.

This operation takes place continuously in a multistage flocculator,making it possible to control the homogenization, concentration anddilution conditions to give the diameter required for the filler-binderflocs before they are incorporated into the head circuits of the paperor board machine.

Stage 4

After the fibers and vegetable fillers have been mixed, it is thenpossible to introduce into the mass the other conventional additives andthe adjuvants required in accordance with the desired objectives.

The weight of the sheet of paper or board can vary between 20 and 500g/m², but for special applications this weight can be much greater, forexample 600 to 1000 g/m² for certain millboards and coverings.

This technology can advantageously be exploited for the manufacture ofpaper and board and especially wrapping paper, paper for corrugatedboard, paper and board for graphic purposes, kraft wrapping paper,pressboard, board for packaging liquids, kraft box-lining paper,newsprint paper, printing-writing substrates, substrates forimpregnation with resins, paper and board for industrial and specialpurposes, paper for domestic purposes, substrates for coating, andcoverings.

The incorporation of the micronized vegetable filler according to theprocess of the invention favors drainage on the paper or board machineand thereby favors productivity. The improvement in drainage is verysubstantial for heavy sheet materials.

Further advantages and characteristics of the invention will beunderstood more clearly from the following description of Examples,which do not imply a limitation but are given by way of illustration,showing the use of these vegetable fillers in the paper sector inparticular.

EXAMPLES 1-3 Preparation of kraft paper

To assess the properties imparted by the vegetable fillers according tothe invention, handsheet samples weighing about 200 g/m² were preparedfor comparison purposes. Example 1 concerns a paper of conventionalformulation according to the prior art and Examples 2 and 3 concernpapers obtained according to the invention. The amounts of the variousingredients (expressed in parts by weight) and the operating proceduresare collated in Table I below. The results obtained are given in TableII below.

Table II shows that the use of the vegetable filler according to theinvention gives the fibrous sheets good overall mechanical strengthproperties, more particularly when the vegetable filler has beenpreflocculated with a binder. The products of Examples 2 and 3 accordingto the invention show a 16% increase in thickness and a 12 to 15%reduction in density compared with the product of Example 1 obtainedaccording to a conventional formulation of the prior art. The productsof Examples 2 and 3 are also found to have improved sizing compared withthe product of Example 1. The sheets of Examples 2 and 3, obtained withthe vegetable filler, are more porous and drain more easily on thehandsheet wire.

                  TABLE I                                                         ______________________________________                                        Composition   Ex. 1 *      Ex. 2 ** Ex. 3 **                                  ______________________________________                                        Softwood kraft pulp (a)                                                                     100          83       83                                        (freeness °SR)                                                                       (23)         (23)     (23)                                      Talc (b)      25-30 (to give                                                                             0        0                                                       15% to 18% of                                                                 residual fillers)                                               Vegetable filler (c)                                                                        0            17 (d)   17 (e)                                    Size (f)      0.3          0.3      0.3                                       Alum          (g)          (g)      (g)                                       Cationic starch                                                                             0.2          0.2      0.2                                       ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) origin: maritime pine;                                                    (b) particle size d.sub.50 = 8-10 micrometers;                                (c) particle size d.sub.95 < 70 micrometers and d.sub.80 > 10 micrometers     density < 300 kg/m.sup.3, origin: maritime pine;                              (d) incorporation into the mass;                                              (e) incorporation into the mass after mixing beforehand with native starc     (0.3 part) and flocculation with polyethyleneimine (0.4 part);                (f) rosin emulsion;                                                           (g) amount sufficient for pH 4.5-4.7.                                    

                  TABLE II                                                        ______________________________________                                        Properties      Ex. 1 *   Ex. 2 ** Ex. 3 **                                   ______________________________________                                        Weight (g/m.sup.2)                                                                            200       201      198                                        Thickness (a)   269       313      312                                        Density (kg/m.sup.3)                                                                          743       642      634                                        Bendtsen permeability to air                                                                  168       340      354                                        (ml/min)                                                                      Tensile strength, average                                                                     11        10.6     11.1                                       MD/CD (kN/m)                                                                  Elongation (%), average                                                                       3.2       2.8      3.2                                        MD/CD                                                                         Energy at break (J/m.sup.2)                                                                   133       121      130                                        Bursting strength (kPa)                                                                       798       772      885                                        Sizing (Cobb) at 60 s (g/m.sup.2)                                                             33        21       20.5                                       Residual fillers (%)                                                                          16.5      0        0                                          ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) in micrometers.                                                      

EXAMPLES 4-5 Preparation of kraft paper for postal bags

For comparison purposes, two samples of kraft paper weighing 120 g/m²,intended for the manufacture of postal bags, were prepared according tothe amounts (expressed in parts by weight) and operating proceduresgiven in Table III below, the product of Example 4 being a paper of aconventional formulation according to the prior art and the product ofExample 5 being a paper containing a vegetable filler according to theinvention, coated with native starch. The results obtained, which arecollated in Table IV below, show that the incorporation of the vegetablefiller according to the invention is very favorable in terms of thethickness (8% increase for Example 5 compared with the control ofExample 4).

                  TABLE III                                                       ______________________________________                                        Composition             Ex. 4 * Ex. 5 **                                      ______________________________________                                        Basic mixture (a)                                                             1) Lightened softwood kraft pulp                                                                      65      67                                            2) Waste unbleached kraft paper                                                                       20      20                                            3) Semibleached chemical pulp                                                                         15      0                                             4) Vegetable filler (based on maritime pine)                                                          0       13                                            (b)                                                                           Additives (c)                                                                 Native starch (d)       0       0.8                                           Cationic flocculant (e) 0       0.03                                          Talc                    23      20                                            Size (f)                0.6     0.6                                           Cationic starch         0.25    0.25                                          Toner                   0.05    0.05                                          Alum                    (g)     (g)                                           ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) amounts introduced, expressed in parts by weight;                         (b) particle size; d.sub.95 < 150 micrometers, d.sub.80 > 10 micrometers,     moisture content < 15% before introduction of the basic mixture into the      aqueous suspension of fibers, density < 300 kg/m.sup.3 ;                      (c) additives introduced into the mass [amounts expressed in parts by         weight per 100 parts of basic mixture (1 + 2 + 3 + 4 = 100)];                 (d) for coating the vegetable filler;                                         (e) polyethyleneimine;                                                        (f) rosin emulsion;                                                           (g) amount sufficient for pH 4.5-5.0.                                    

                  TABLE IV                                                        ______________________________________                                        Properties          Ex. 4 *  Ex. 5 **                                         ______________________________________                                        Weight (g/m.sup.2)  87       87                                               Thickness (a)       151      163                                              Bulk (cm.sup.3 /g)  1.74     1.87                                             Bendtsen porosity (ml/min)                                                                        2000     2300                                             Breaking length (m) 4580     4620                                             Burst factor (kPa · m.sup.2 /g)                                                          3.22     3.48                                             Tear factor (mN · m.sup.2 /g)                                                            1280     1210                                             Sizing (Cobb) at 60 s (g/m.sup.2)                                             recto               18.9     17.8                                             verso               21.7     20.3                                             Whiteness (photovolt)                                                                             36       36                                               Retention (%)                                                                 fibers              98       98                                               vegetable filler    --       80                                               talc                59       65                                               ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) in micrometers.                                                      

OBJECTIVE

One of the essential properties of kraft paper for postal bags, apartfrom the customary mechanical strength properties and the appearance ofa friction-glazed kraft paper for this type of use (tear factor, burstfactor, tensile strength, uniformity and level of gloss) is the bulking,which plays a part in the machinability of the paper converted on modernequipment for the production of envelope-bags, and also in the marketingimpact.

RESULTS

The introduction of vegetable material coated with native starch favorsthe thickness of the sheet: an increase of about 8% without modifyingthe mechanical characteristics of the paper. The good retention of thevegetable filler according to the invention should be noted.

Also notable are the good sizing performance characteristics and thesubstantial increase in thickness (the thickness is the converse of thebulk), this having a very favorable effect on the stiffness, whichvaries as the cube of the thickness.

ECONOMIC ADVANTAGES

The reduction in the cost of the product according to Example 5 comparedwith the control of Example 4 is of the order of 6%, without allowingfor the increase in productivity due to better drainage.

EXAMPLES 6-8 Preparation of paper for coating with plastic

Sheets of paper weighing about 210 g/m² were prepared according to theamounts of ingredients (expressed in parts by weight) and operatingprocedures in Table V below. The results obtained have been collated inTable VI below.

These results show that, in this specific case, the products of Examples7 and 8, which contain a vegetable filler according to the invention,are 30 to 40% less dense than the product of Example 6 obtainedaccording to a formulation of the prior art.

The compositions of Examples 7 and 8 are very economical (sawmill wasteand tree stumps) with less synthetic binder, which explains the slightlyinferior mechanical strength properties, but these physicalcharacteristics are well in excess of the conventional requirements forbases to be coated with plastics, intended for the manufacture ofbuilding materials.

The heat resistance of the sheets with vegetable fillers according toExamples 7 and 8 is also found to be good. The substantial increase inthickness and the reduction in density affect the acoustic attenuationprovided by the material or covering.

                  TABLE V                                                         ______________________________________                                        Composition     Ex. 6 *   Ex. 7 **  Ex. 8 **                                  ______________________________________                                        Unbleached softwood kraft                                                                     100       50        50                                        pulp (a)        (20-22)   (20-22)   (20-22)                                   (freeness °SR)                                                         Glass fibers    6         6         6                                         Talc (b)        45 to 55  0         0                                                         (for                                                                          30-35% of                                                                     residual                                                                      fillers)                                                      Vegetable filler (c)                                                                          0         50 (d)    50 (e)                                    Acrylic binder  10        8         8                                         Starch binder   0         1         1                                         Cationic polyamide                                                                            0         1         1                                         Cationic starch 0         0.2       0.2                                       Size (f)        1.2       1.2       1.2                                       Alum            (g)       (g)       (g)                                       ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) origin: maritime pine;                                                    (b) particle size d.sub.50 = 8-10 micrometers;                                (c) particle size d.sub.95 < 100 micrometers and d.sub.80 > 10                micrometers, moisture content < 15% before introduction into the aqueous      suspension of fibers (for a mixture of sawmill waste and maritime pine        tree stump in the weight ratio 80-20), density < 300 kg/m.sup.3 ;             (d) incorporation into the mass;                                              (e) incorporation into the mass after prior mixing with native starch (0.     part) and flocculation with polyethyleneimine;                                (f) rosin emulsion;                                                           (g) amount sufficient for pH 6.0-6.5.                                    

                  TABLE VI                                                        ______________________________________                                        Properties      Ex. 6 *   Ex. 7 ** Ex. 8 **                                   ______________________________________                                        Weight (g/m.sup.2)                                                                            215       208      207                                        Thickness (a)   270       398      395                                        Density (kg/m.sup.3)                                                                          796       522      524                                        Bendtsen permeability to                                                                      320       1550     1520                                       air (ml/min)                                                                  Tensile strength, average                                                                     7.95      6.22     6.98                                       MD/CD (kN/m)                                                                  Breaking energy (J/m.sup.2)                                                                   99        78       87                                         Bursting strength (kPa)                                                                       570       539      565                                        Sizing (Cobb) at 60 s (g/m.sup.2)                                                             20        18.5     18.5                                       Residual fillers (%)                                                                          32        0        0                                          Dimensional stability                                                         oven drying (105° C., 1 h)                                                             0.7% (b)  0%       0%                                         soaking in water (1 h)                                                                        0.6       0.6      0.6                                        ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) in micrometers;                                                           (b) shrinkage.                                                           

EXAMPLES 9-10 Preparation of featherweight kraft board

Examples 9 and 10 below illustrate the advantages of micronizedvegetable filler according to the invention (cf. Example 10 comparedwith the control of Example 9), used in a fibrous composition ofunbleached kraft pulp and chemicomechanical pulp for the manufacture ofmulti-ply boards (especially so-called wood board and gray board).

It is found that replacing about 10% of chemicomechanical pulp(abbreviated to "CTMP") with micronized vegetable filler coated withnative starch does not affect the mechanical performance characteristicsof the final sheet product, in particular the stiffness, for anequivalent or slightly greater bulk. The material obtained according toExample 10 of the invention has a greater porosity and better drainagethan the control of Example 9. The improvement in drainage represents asubstantial advantage in terms of productivity; overall, the compositionof Example 10 is 5% more economical than that of the control of Example9.

The procedures for obtaining the boards of Examples 9 and 10 are shownin Table VII below and the properties of these boards are collated inTable VIII below.

                  TABLE VII                                                       ______________________________________                                        Composition         Ex. 9 *  Ex. 10 **                                        ______________________________________                                        Basic mixture (a)                                                             1) Unbleached softwood kraft pulp                                                                   50      50                                              refined to 20° SR                                                      2) CTMP               50      39                                              3) Vegetable filler (based on                                                                       0       11                                              maritime pine) (b)                                                            Additives (c)                                                                 Native starch (d)     0       0.7                                             Cationic flocculant (e)                                                                             0       0.02                                            Talc                  35      35                                              Size (f)              0.6     0.6                                             Alum                  (g)     (g)                                             ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) amounts introduced, expressed in parts by weight;                         (b) particle size: d.sub.95 < 100 micrometers, d.sub.80 > 10 micrometers,     moisture content < 15% before introduction of the basic mixture into the      aqueous suspension of fibers, density < 300 kg/m.sup.3 ; the vegetable        filler is a mixture obtained from sawdust and planing chips of maritime       pine;                                                                         (c) additives introduced into the masss [amounts expressed in parts by        weight per 100 parts of basic mixture (1 + 2 + 3 = 100)];                     (d) for coating the vegetable filler;                                         (e) polyethyleneimine;                                                        (f) rosin emulsion;                                                           (g) amount sufficient for pH 4.5-5.0.                                    

                  TABLE VIII                                                      ______________________________________                                        Properties          Ex. 9 *  Ex. 10 **                                        ______________________________________                                        Weight (g/m.sup.2)  252      254                                              Thickness (a)       455      472                                              Bulk (cm.sup.3 /g)  1.80     1.86                                             Bendtsen porosity (ml/min)                                                                        680      1075                                             Breaking length (m) 3120     3090                                             Burst factor (kPa · m.sup.2 /g)                                                          1.92     1.89                                             Tear factor (mN · m.sup.2 /g)                                                            1080     1075                                             Sizing (Cobb) at 60 s (g/m.sup.2)                                             recto               20.2     19.6                                             verso               20.4     18.6                                             Whiteness (photovolt)                                                                             44       46                                               Buchel stiffness (mN)                                                                             145      165                                              Retention (%)                                                                 fibers              97.5     98.0                                             vegetable filler    --       88.0                                             talc                65.0     70.0                                             ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) in micrometers.                                                      

EXAMPLES 11-12 Preparation of substrate for impregnation

Substrates for impregnation with phenolic resin, intended for themanufacture of laminated panels, were prepared, the product of Example11 being obtained according to a conventional formulation of the priorart and the product of Example 12 being obtained with a vegetable filleraccording to the invention. The amounts of the ingredients (expressed inparts by weight) and the operating procedures have been collated inTable IX below. The results of the tests are given in Table X below.

Table X shows that the product of Example 12 according to the inventionis 30% thicker and 21% less dense than the product of Example 11. Thissituation is particularly advantageous in that it enables the number ofsheets forming the inner cores of laminated panels to be reduced.

                  TABLE IX                                                        ______________________________________                                        Composition       Ex. 11 * Ex. 12 **                                          ______________________________________                                        Softwood kraft pulp                                                                             40       40                                                 (maritime pine)                                                               Eucalyptus kraft pulp                                                                           60       20                                                 Freeness (°SR)                                                                           22       22                                                 Vegetable fillers 0        40                                                 d.sub.98 < 70 micrometers                                                     Antifoam          0.1      0.1                                                ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention.                                   

                  TABLE X                                                         ______________________________________                                        Properties          Ex. 11 * Ex. 12 **                                        ______________________________________                                        Weight (g/m.sup.2)  180      182                                              Thickness (micrometers)                                                                           295      382                                              Bulk (cm.sup.3 /g)  1.64     2.1                                              Density (kg/m.sup.3)                                                                              610      476                                              Porosity (s)        14-18    10-12                                            Capillary rise in 10 minutes                                                                      40 to 50 40 to 50                                         (mm)                                                                          Dry tensile strength, average                                                                     6.1      5.8                                              MD/CD (kN/m)                                                                  Wet tensile strength (MD)                                                                         0.6      0.5                                              ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention.                                   

EXAMPLE 13

A base intended for an industrial composite is coated with a compositioncomprising 100 parts by dry weight of the hot-melt Mobil EF 78 BE and 20parts by dry weight of vegetable filler (particle size d₉₅ <50micrometers, d₈₀ <10 micrometers, moisture content less than 15% beforeintroduction into the aqueous suspension of fiber), the said vegetablefiller being introduced after the hot-melt has been melted. The productobtained has an improved opacity.

EXAMPLES 14-15 Preparation of substrate for impregnation to makelaminated panels

Example 14 (prepared by a conventional technique of the prior art) andExample 15 (prepared by the process of the invention with a micronizedvegetable filler) were carried out to give a kraft substrate intendedfor subsequent impregnation with a phenolic resin for the preparation oflaminated panels.

The fundamental properties desired for such a substrate are: uniformformation of the fibrous sheet material and appropriate porosity andcapillary rise for the most uniform resin pick-up possible at thedesired level, having regard to the properties required for laminatedpanels.

The composition of the ingredients and the procedures for obtaining thesheets of Example 14 (control) and Example 15 (according to theinvention) are collated in Table XI below. The properties of thecorresponding sheets obtained are shown in Table XII below.

The numerical values given in Tables XI and XII clearly show theadvantages brought by using the micronized vegetable filler according tothe invention, namely:

the distinct improvement in the bulk (+18% when comparing the product ofExample 15 with the control of Example 14);

the replacement of the absorbent fibers (junkers fibers), which areexpensive, with conventional softwood fibers, on the one hand, and withthe vegetable filler, on the other, both of hwich are less expensivethan the said absorbent fibers; and

the possibility of using less refined fibers (freeness of 30° SR for thefibers of Example 15 instead of 26° SR for the fibers of Example 14).

When comparing the product of Example 15 with the control sheet ofExample 14, these advantages afford an appreciable increase inproductivity in terms of (i) the production of the substrate forimpregnation on the paper machine (in view of the improved drainage),and (ii) the impregnation device when the phenolic resin is applied.

In brief, according to the invention, it is found that the cost ofpreparing the sheet 15 is at least 15% less than that of the sheet 14.

                  TABLE XI                                                        ______________________________________                                        Composition          Ex. 14 * Ex. 15 **                                       ______________________________________                                        Basic mixture (a)                                                             1) Unbleached softwood kraft pulp                                                                  65       80                                              2) Junkers pulp (absorbent grade)                                                                  35       0                                               Freeness (°SR) for (1 + 2)                                                                  26° SR                                                                          30° SR                                   3) Vegetable filler (based on                                                                      0        20                                              maritime pine) (b)                                                            Additives (c)                                                                 Native starch (d)    0        1                                               Cationic flocculant (e)                                                                            0        0.03                                            ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) amounts introduced, expressed in parts by weight;                         (b) particle size: d.sub.95 < 100 micrometers, d.sub.80 > 10 micrometers,     moisture content less than 15% before introduction into the aqueous           suspension of fibers;                                                         (c) additives introduced into the mass [amounts expressed in parts by         weight per 100 parts of basic mixture (1 + 2 + 3 = 100)];                     (d) for coating the vegetable filler;                                         (e) polyethyleneimine.                                                   

                  TABLE XII                                                       ______________________________________                                        Properties          Ex. 14 * Ex. 15 **                                        ______________________________________                                        Weight (g/m.sup.2)  181      180                                              Thickness (a)       285      335                                              Bulk (cm.sup.3 /g)  1.57     1.86                                             Bendtsen porosity (ml/min)                                                                        590      850                                              Breaking length (m) 4980     4890                                             Burst factor (kPa · m.sup.2 /g)                                                          3.78     3.60                                             Tear factor (mN · m.sup.2 /g)                                                            1470     1480                                             5 mm capillary rise (in                                                                           25.2     38                                               minutes)                                                                      Water drop (s)                                                                recto               5.0      2.0                                              verso               4.5      2.5                                              Retention (%)       --       79                                               vegetable filler                                                              ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) in micrometers.                                                      

EXAMPLES 16-17 Preparation of kraft liner

Example 16 (prepared by a conventional technique of the prior art) andExample 17 (prepared by the process of the invention with a micronizedvegetable filler) were carried out to give a sheet of kraft liner. Theaim was to increase the bulk while at the same time preserving thephysical properties of the control sheet of Example 16.

The composition of the ingredients and the procedures for obtaining thesheets of Example 16 (control) and Example 17 (according to theinvention) are collated in Table XIII below. The properties of thecorresponding sheets obtained are shown in Table XIV below.

The numerical values given in Tables XIII and XIV show that the sheet ofExample 17 exhibits a 12% improvement in the bulk with a 5% reduction inthe bursting strength. This reduction in strength can be mitigated(taking into account the wide tolerance of the porosity of the fibroussheet product of Example 17) by means of a small increase in the °SR ofthe fibers.

                  TABLE XIII                                                      ______________________________________                                        Composition          Ex. 16 * Ex. 17 **                                       ______________________________________                                        Basic mixture (a)                                                             1) Unbleached softwood kraft pulp                                                                  75       60                                              refined to 20° SR                                                      2) Waste paper pulp (OCC)                                                                          25       25                                              3) Vegetable filler (based on                                                                      0        10                                              maritime pine) (b)                                                            Additives (c)                                                                 Starch               0        1.1                                             Cationic flocculant (e)                                                                            0        0.02                                            Size (f)             0.6      0.6                                             Alum                 (g)      (g)                                             ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) amounts introduced, expressed in parts by weight;                         (b) particle size: d.sub.95 < 100 micrometers, d.sub.80 > 10 micrometers,     moisture content < 15% before introduction of the basic mixture into the      aqueous suspension of fibers, density = 195 kg/m.sup.3 ;                      (c) additives introduced into the mass [amounts expressed in parts by         weight per 100 parts of basic mixture (1 + 2 + 3 + 4 = 100)], density 195     kg/m.sup.3, d.sub.95 < 100 micrometers;                                       (e) polyethyleneimine;                                                        (f) rosin emulsion;                                                           (g) amount sufficient for pH 4.5- 5.0.                                   

                  TABLE XIV                                                       ______________________________________                                        Properties          Ex. 16 * Ex. 17 **                                        ______________________________________                                        Weight (g/m.sup.2)  152      151                                              Thickness (a)       238      266                                              Bulk (cm.sup.3 /g)  1.56     1.76                                             Bendtsen porosity (ml/min)                                                                        500      1000                                             Breaking length (m) 4670     4595                                             Burst factor (kPa · m.sup.2 /g)                                                          3.82     3.65                                             Tear factor (mN · m.sup.2 /g)                                                            1570     1480                                             Sizing (Cobb) at 60 s (g/m.sup.2)                                             recto               20.2     20.2                                             verso               24.8     21.8                                             Retention (%)                                                                 fibers              --       97.6                                             vegetable filler    --       85.0                                             ______________________________________                                         Notes                                                                         * conventional formulation according to the prior art;                        ** Example according to the invention;                                        (a) in micrometers.                                                      

I claim:
 1. A method for the preparation of a fibrous sheet material bya paperworking technique, comprising:providing an aqueous dispersioncontaining fibers: producing pulverulent vegetable filler by agrinding-micronization operation of planings from vegetable materialhaving a mean particle size of less than 5 mm and a residual moisturecontent of less than 20% by weight; said vegetable filler having adensity of less than 500 Kg/m³ and a particle size wherein at least 95%by weight of the vegetable filler has a dimension size lower than 150micrometers and more than 80% by weight of the vegetable filler has adimension size larger than 10 micrometers; and introducing saidvegetable filler into said aqueous solution.
 2. A method as claimed inclaim 1, wherein said vegetable filler has a density of less than 300kg/m³.
 3. A process as claimed in claim 1, wherein the said vegetablematerial comprising a vegetable waste selected from the group consistingof wood, bark and cereal wastes is obtained by means of agrinding-micronization operation of said vegetable waste having a meanparticle size of less than 5 mm and a residual moisture content of lessthan 20%.
 4. A method as claimed in claim 1, wherein said vegetablematerial comprises a vegetable waste having a residual moisture contentof less than 15%.
 5. A method as claimed in claim 1, wherein at least95% of the particles of said vegetable filler have dimensions smallerthan 100 micrometers.